The great wall of China is truly a marvel of human engineering. The wall itself stretches for 3,890 miles with an additional 1,610 miles of trenches, rivers, and hills. The wall was begun in the 5th century BC and construction continued into the 16th century. In the beginning, construction was simple. The first sections of the wall were crude barriers made of rammed earth, wood and stones. In the 15th century, larger, more elaborate sections of wall were constructed from bricks and stone as a defense against Mongol raids.
While the improved great wall prevented the Mongols from re-conquering China as they had previously in the 13th century, it did not keep them out completely. A band of mongols was able to sneak through and capture a 15th century Ming Dynasty emperor and hold him captive for a year. Then, in 1644, internal rebellions destroyed the ruling Ming Dynasty and the Manchu were able to enter China through the great wall’s gates.
Urban space myth. Can the great wall be seen from the moon? No. Is the great wall one of the only man made structures that can be seen from space? Again, no. But an astronaut aboard the space station did get a grainy, indistinct picture of it using a camera with a high power lens.